This invention relates to a rotating machine such as a centrifuge. More particularly, this invention relates to a liquid phase discharge port for a rotating machine such as a centrifuge. This invention also relates to an associated method of effluent discharge from a rotating machine.
In bowl of a decanter centrifuge, solid-liquid separation takes place in a rotating pool that is maintained by a set of semi-circular weirs. The settled solid cake (hereafter referred as heavy phase) is conveyed toward a conical beach at one end of the rotating bowl by a screw conveyor, which rotates at a differential speed compared with the bowl, while the clarified liquid containing unsettled fine solids or the light phase (hereafter simply referred as liquid or liquid phase) overflows the weirs at the large end of the machine opposite the conical beach.
It is well known that a portion of the total hydraulic power consumed during operation of a centrifuge is wasted as kinetic energy of the discharged effluent liquid and the remaining portion wasted in dissipation. The total hydraulic power consumed is proportional to the density of the clarified liquid, the volumetric flow rate of the liquid, the rotational speed of the bowl to the second power, and the discharge radius of the pool to the second power. To that end, it is important to operate the centrifuge with the lowest possible speed and centrifugal gravity while still achieving process separation.
Another problem in centrifuge operation is related to pool level adjustment. There may be geometric constraints at the effluent bowl head, which limit the radius of the weirs. This problem is especially acute when the pool is deep especially at the spill point of the conical beach.
The physical principle of using reaction torque from a discharged high-velocity jet is well known but has not been successfully implemented to recover power from decanter centrifuges. For example, U.S. Pat. No. 5,147,277 discusses a vane apparatus wherein the clarified effluent leaving an opening of the bowl head is channeled into a plurality of channels formed by adjacent vanes. The flow turns from an axial direction to a radially inward direction along the vanes. As the fluid reaches the smaller radius of the vane apparatus, it is redirected by the vanes to flow circumferentially in a direction opposite to the direction of rotation of the centrifuge bowl.
The discharge radius of the vane apparatus of U.S. Pat. No. 5,147,277 is small to conserve power and the discharge radius is approximately at the spillover radius of the conical beach. This design incurs high pressure or head loss in part owing to friction from the large surface area of the vanes with which the discharging fluid is in contact.